1. Field of the Invention
The present invention relates to a system and method of compensating for variations in energy output of a laser. More particularly, the present invention relates to a system and method for adjusting mask dimensions to compensate for variations in energy output in an excimer laser used in ablating an inkjet nozzle plate.
2. Description of the Related Art
Excimer lasers are widely used in industry to form minuscule structures in objects due to their high-energy output and precision. Frequently, a mask is employed in the laser ablation process so that the laser may ablate very complex structures. Excimer lasers have also found a place in the manufacture of inkjet nozzle plates. When manufacturing a nozzle plate for an inkjet printer it is necessary to form precise nozzle holes, firing chambers and channels. The quality of the ultimate printing is directly effected by the precision of the ablating of the nozzle plate by the excimer laser.
In recent years users of color inkjet printers have seen significant improvements in the resolution of images created by these printers. At present near photographic image quality is possible using four ink color inkjet printers. These high resolution color images are possible in part due to the ability to print 600 or more dots per inch ("dpi"). In order to achieve 600 dpi, the print head must have a nozzle concentration of 600 nozzles openings per inch since a single nozzle is used to create a single drop of ink on the print medium. At this nozzle concentration, the nozzle diameters must be on the order of 16 microns in diameter.
In order to generate nozzle openings of this diameter, various types of lasers have been successfully employed to create the nozzle openings, firing chambers and ink channels as disclosed in the prior art discussed below.
U.S. Pat. No. 5,305,015 to Schantz et al. discloses an inkjet print head made of polymer based flexible tape which is laser ablated to form inkjet orifices, vaporization channels and ink channels. A mask is used in the ablating process to produce the features required in the print head.
U.S. Pat. No. 5,378,137 to Asakawa et al. discloses using a mask having opaque dots situated around the edge of holes in the mask so that when a YAG or excimer laser beam is shown through a hole of the mask, the energy intensity of the laser beam at the edges of the hole is reduced. By allowing the full energy of the laser to strike the workpiece in the center of the hole and only partial energy to travel through the edges, a modified tapered hole may be created in the work piece. Using the disclosures of this patent the angle of taper of holes in structures may be adjusted.
U.S. Pat. No. 4,786,358 to Yamazaki et al. discloses an improved method for forming a pattern on a substrate coated with a film. The substrate is irradiated with a laser beam that is shaped through a mask, and a portion of the film is removed by the energy of the laser beam to produce the desired pattern.
U.S. Pat. No. 4,108,659 to Dini discloses a process for engraving printing surfaces with unmodulated energy beams by interposing a variable reflectivity mask between the energy beam source and the printing surface. The local reflectivity of the mask varies in correspondence with the tone gradation of the original to be printed, and may be formed by conventional photographic techniques, directly on the surface or on a substrate carrier through which the energy beam passes.
However, due to anomalies in the manufacturing of lens and the optical delivery system used in the laser system, the energy output is not consistent throughout the entire width and length of the laser beam. This results in the excimer laser used to ablate the nozzle plates having characteristic energy distribution along the beam profile that creates variations in exit hole diameters and variations in ablated depth from the end to the middle of the beam. With such anomalies, nozzle holes generated will be larger in one part of the nozzle plate and smaller in other parts. Also other features of the nozzle plate and print head would vary such as firing chamber size and channel depth. Thus, the quality of printing would be adversely effected due to the variation in the feature size.
In addition, variations in the nozzle and print head features further effect the performance of the inkjet printer. For example, when nozzle and channel sizes vary the refill time for the firing (vaporizer) chamber will also vary which will force the designer of the inkjet printer to slow the print speed in order to insure that all the firing chambers can be filled before being fired again. Further, variations in the nozzles and print head features will have a direct impact on the drop mass of ink deposited on the print medium and the velocity at which the ink is deposited. In turn, both the drop mass and velocity directly effect the image quality seen by the user.
Therefore, a system and method is needed that can compensate for the anomalies in energy output for a laser system so that uniform structures may be generated throughout a workpiece. This need for consistent structures in nozzle plates and print heads becomes even more critical as structures become smaller in the future in order to achieve still higher resolutions of 1,200 or 2,400 dpi. At these high resolutions, a one to two micron variation in nozzle diameter will cause a 25% or more variation in structure dimensions of the nozzle plate and produce variations in print quality that would be detectable by a user.